It has been a goal in the industry to provide a safe and effective way to handle toxic, flammable, corrosive gases at sub-atmospheric conditions. In particular, these gases include dopant gases. Generally, dopant gases are stored in compressed gas cylinders at pressures equal to the individual gases vapor pressure at a given or at a specific pressure depending upon the properties of the specific gas. The gases serve as a source of dopant material for the manufacturing of semiconductor devices. These dopant gases are used in a tool called an ion implanter. Ion implanters are located within in the fabrication area of a semiconductor production facility where several hundreds or even thousands of personnel are engaged in the semiconductor manufacturing process. These tools are operated at very high voltages, typically up to several thousand kilovolts. Due to these high voltages, the dopant source gases must be located at or within the tool itself (most other semiconductor tools locate source gases outside of the personnel or main production area). One distinct characteristic of the ion implant tools is that they operate as sub-atmospheric pressure. Utilization of the vacuum present at the tool to delivery product from the cylinder creates a safer package in that product cannot be removed from the cylinder package until a vacuum is applied. This vacuum delivery concept prevents accidental exposure from the pressurized gas.
Currently, there are believed to be three distinct methods for solving the problems associated with the sub-atmospheric delivery of dopant gases. The first involves filling a compressed gas cylinder with a physical adsorbent material (beaded activated carbon), and reversibly adsorbing the dopant gases onto the material. This concept is commonly known as the SDS™ technology. The desorption process involves applying a vacuum or heat to the adsorbent material/cylinder. In practice, vacuum from the ion implanter is used to desorb the gas from the solid-phase adsorbent. There are certain limitations associated with the problems with the SDS technology, and they include: 1) the adsorbent material has a finite loading capacity thereby limiting the amount of product available in a given size cylinder; 2) the desorption process can be initiated by exposing the cylinder package to heat, thereby causing the cylinders to reach and deliver gases at atmospheric and super-atmospheric pressures when the cylinder is exposed to temperatures greater than 70 degrees F., which are common in many cylinder warehouse locations; 3) the purity of the gas delivered from the cylinder can be comprised due to adsorption/desorption of the other materials/gases on the adsorbent material; and 4) adsorbent attrition can lead to particulate contamination in the gas delivery system.
A second method for solving the problems associated with the sub-atmospheric delivery of dopant gases involves the use of a mechanical regulator or check valve to control/deliver the product sub-atmospherically. These regulating devices are set to deliver or open when sub-atmospheric or vacuum conditions are applied to the device. The regulating devices are located upstream of a conventional on/off cylinder valve seat mechanism. The exact location of these upstream regulating devices can be in the valve body, in the neck cavity, inside the cylinder itself, or combinations of all three locations. In each case the regulating device is located upstream of the cylinder valve seat with respect to flow of gas from the interior of the cylinder to the delivery port.
U.S. Pat. No. 5,937,895 discloses a regulator in the form of dispensing check valve and a flow restriction arrangement to provide a virtually fail safe system for preventing hazardous discharge of fluid from a pressurized cylinder or tank. U.S. Pat. No. 6,045,115 discloses a flow restrictor to provide a capillary size opening that minimizes any discharge of toxic gases from compressed gas cylinders in the unlikely event of the control valve or regulator failure. Both of these disclosures provide for a sub-atmospheric delivery regulating device that is located upstream of a valve seat with regard to the flow of gas through a valve. It is believed that these disclosures provide a regulating device with significant limitations regarding the maximum inlet pressure (or cylinder storage pressure) must be at or below approximately 600 psig, and the regulating device is preset for a given pressure (which is not adjustable).
U.S. Pat. Nos. 6,089,027 and 6,101,816 are both related to a fluid storage and dispensing system comprising a vessel for holding a desired pressure. The vessel has a pressure regulator, e.g., a single-stage or multi-stage regulator, associated with a port of the vessel, and set at a predetermined pressure. A dispensing assembly, e.g., including a flow control means such as a valve, is arranged in gas/vapor flow communication with the regulator, whereby the opening of the valve effects dispensing of gas/vapor from the vessel. The fluid in the vessel may be constituted by a liquid that is confined in the vessel at a pressure in excess of its liquefaction pressure at prevailing temperature conditions, e.g., ambient (room) temperature. The '027 patent discloses a multi-stage regulator on the upstream side of the valve control means.
The above patents disclose locating the regulating devices upstream of the valve seat with respect to the flow of gas from the interior of the cylinder to the delivery port. However, the regulating devices can be located in the valve body, in the neck cavity, inside the cylinder itself, or a combination of all three of these locations.
A third method for solving the problems associated with the sub-atmospheric delivery of dopant gases involves the use of a single regulator located downstream mechanical regulator or check valve to control/deliver the product sub-atmospherically. U.S. Pat. No. 6,314,986 discloses a modular gas control device for use with a compressed gas cylinder comprises a primary module and a secondary module mounted on the primary module. This patent discloses the use of a single regulator located downstream of the main cylinder shut-off valve. The regulator is located within the valve body and is adjustable to deliver any desired outlet pressure from sub- to super-atmospheric pressure. The shut-off valve has its internal and seat mechanism located upstream of the regulator. A single regulator is disclosed. There are certain potential problems associated with this method. For example, potential high leak rate and pressure rise in the event the regulator failure may occur. Also, the single regulator may have difficulty controlling flow over large inlet pressure ranges.
It is an object of this invention to limit or prevent the release of toxic gases in the event of a valve or conduit failure.
Another object of this invention is to enable the storage of higher pressures in the gas cylinders. The higher pressure provides a greater amount of product to be contained in the cylinder, thereby providing greater productivity and lower cost for the customer.
Another object is to provide greater protection from exposing the cylinder valve seat to air contamination by the additional regulator(s).
Yet another object is to provide a pressurized gas cylinder even greater protection from exposing the pressurized gas to the atmosphere due to the limited flow capacity of the specialized capillaries.
Yet another object is to provide a regulating device downstream of the valve seat with an optional control to adjust the outlet pressure from sub-atmospheric to any desirable pressure less than or equal to the outlet pressure of the regulator located upstream of the valve seat.